Geochemistry of clay dunes and associated pan in the Senegal Delta (Mauritania)

Abstract

Aeolian deflation is very active in the Senegal delta and results in the formation of many clay dunes with high salt concentration. The chemistry of soil and groundwater was studied along a sequence from a pan to the associated clay dune in the Diawling park. Equilibria computation and field and SEM observations indicates that the changes observed in the chemical facies of the solution are due to the following precipitation sequence : calcite>gypsum>halite. A progressive but significant fixing of sodium onto the clay particles is observed. However, the calcite deposite in the soil is limited by exhibition of the potentiel acidity arising from the former mangrove. It locally results in high equilibrating CO2 pressure. This study provided an opportunity to test succesfully a new extension to the Debye-Hückel law for concentrated chlorurated sodic waters. (Résumé d'auteur